Adults who consume high levels of sugar have significantly elevated levels of several risk factors for heart disease, according to a new study by a team of researchers at the University of California, Davis and in Japan.

The study results suggest that U.S. dietary guidelines for sugar may be lax and should be reconsidered, the researchers say. Their findings were reported online in the Journal of Clinical Endocrinology & Metabolism, and will appear in the journal's October print edition.

"While there is evidence that people who consume sugar are more likely to have heart disease or diabetes, it has been controversial as to whether high-sugar diets may actually promote these diseases,” said Kimber Stanhope, the study's senior author and a research scientist at UC Davis.

"Our new findings demonstrate that several factors associated with an elevated risk for cardiovascular disease were increased in individuals who consumed 25 percent of their calories as fructose or high fructose corn syrup," Stanhope added.

In this study, the researchers examined 48 adult participants between the ages of 18 and 40 years. For five weeks before the study, subjects were asked to limit daily consumption of sugar-containing beverages to one 8-ounce serving of fruit juice. The participants were then divided into three groups, each group consuming 25 percent of their daily calories as fructose, high fructose corn syrup or glucose.

The researchers found that within two weeks, study participants consuming fructose or high fructose corn syrup exhibited increased bloodstream concentrations of three known risk factors for heart disease: LDL cholesterol, triglycerides and a protein known as apolipoprotein-B, which can lead to plaque buildup in arteries.

These same risk factors for heart disease did not increase in participants who consumed glucose. (In this study, the researchers were looking at the participants consuming glucose as a control group, against which results from the other two groups could be compared.)

Stanhope noted that the American Heart Association recommends that people consume only five percent of their daily calories as added sugar, but the federal Dietary Guidelines for Americans 2010 suggest an upper limit of 25 percent or less.

Funding for the study was provided by the National Institutes of Health.

The UC Davis researchers on the study include Stanhope and professor Peter Havel, both in the Department of Molecular Biosciences of the School of Veterinary Medicine and in the Department of Nutrition; adjunct professor Nancy Keim of the U.S. Department of Agriculture's Western Human Nutrition Research Center; assistant professor Valentina Medici of the School of Medicine; Andrew Bremer, now assistant professor of pediatrics at Vanderbilt University; and staff researchers Guoxia Chen, Tak Hou Fong, Vivien Lee and Roseanne Menorca. Researchers from Japan included Katsuyuki Nakajima and Takamitsu Nakano, both of Otsuka Pharmaceutical Co. in Tokyo, and Yasuki Ito of Denka Seiken Co. in Tokyo.